STOP Early Journal Content on JSTOR, Free to Anyone in the World This article is one of nearly 500,000 scholarly works digitized and made freely available to everyone in the world byJSTOR. Known as the Early Journal Content, this set of works include research articles, news, letters, and other writings published in more than 200 of the oldest leading academic journals. The works date from the mid-seventeenth to the early twentieth centuries. We encourage people to read and share the Early Journal Content openly and to tell others that this resource exists. People may post this content online or redistribute in any way for non-commercial purposes. Read more about Early Journal Content at http://about.istor.org/participate-istor/individuals/early- journal-content . JSTOR is a digital library of academic journals, books, and primary source objects. JSTOR helps people discover, use, and build upon a wide range of content through a powerful research and teaching platform, and preserves this content for future generations. JSTOR is part of ITHAKA, a not-for-profit organization that also includes Ithaka S+R and Portico. For more information about JSTOR, please contact firstname.lastname@example.org. 96 REVIEWS flows have covered the region. Later erosion has partly uncovered the older sediments and intrusives. The ores are principally magnetite and hematite with a small amount of limonite, and occur (a) as fissure veins in the andesite, (6) as fissure veins and replacement deposits along the contact of the andesite and lime- stone, and (c) as a cement in a Cretaceous quartzite-breccia. J. C. J. Geology of the Rangeley Oil District, Colorado. By Hoyt S. Gale. Bulletin 350, U. S. Geological Survey. A small field at the western border of Colorado is described where con- siderable prospecting for oil has been going on with some success. The rocks are principally Cretaceous and Tertiary. The base of the Wasatch formation (Tertiary) rests with apparent conformity upon the top of the Mesaverde formation (Cretaceous), but the absence of formations found between them elsewhere in Colorado indicates a non-conformity here. The structure is a quaquaversal fold with little evidence of faulting. The oil occurs presumably in lenses in the Mancos (Cretaceous) shale. J. C. J.